Cutting oil composition



-er'ations. odoriferous'compoundsunder the conditions prevailing 2-,790','77s CUTTING OIL eoMPosiTIoN llarrison TM, Stine, I-iyn1dhurst, Ohio, 'assig'nor to The StandardGib-Company, Cleveland, Ohio, a corporation ofOhio 'NoDrawing. Application June 13, 1952, Serial No. 293,444

7 Claims. (Cl. 252- 45) The present invention relatesto a cutting oil concentrat'e, cutting oils containing such a concentrate and characterized by a-uniq'ue combinationof superior cut- United States Patent therein have been suggested heretofore as cutting oils.

Such oils also frequently contain chlorine and a fat such as lard'oil. It is believed that the sulfur, to be efii'ective in improving the cutting ability of a cutting oil, must be in an active form, i. e., not bound to a carbon atom, which can react with metal being machined under the conditions existing at thepoint of contact between the tool and the machined metal. Heretofore, the amount of active sulfur'which could beincorporated into an oil has been dependent largely upon the" solubility of free sulfur in'the oil and upon'the amount of sulfur which can be chemically combined but not bound to a carbon atom.

A great many suggestions have been made heretofore for increasing the activesulfur content of cutting oils. In some instances, these suggestions have resulted in oils having excellent cutting abilitybut poor odor'characteristics and/or stability. In other instances, they have resulted in oils of acceptable odorbut of "poor cutting ability. in still other instances the oils developed' have "been found to 'be too dark or opaque topermit adequate viewing of the work during a *machining operation.

Generallyit'has been found that some compromise must be made amon odor,stability, optical density and cutting 1 ability factors, the cutting ability being improved with an increase in sulfur contentat the'expense, however, of odor, stability and opacity. To the "best 'of applicants knowledge, no cuttingoil having optimum cutting ability and'odor has ever been developed heretofore.

The odor characteristics of'a cutting oil are not necessarily apparent upon an examination of the oil as'produced or supplied to a user. In many instances, odors are developed only when the'oil is used in machining op- This is apparently due to the formation of at the cutting tool. If the cutting oil 'develo'ps an unpleasant or obnoxious odor during use, it makes' no difference howgood the oil is'fr'om thes'tandpoint of cutting ability, i. e.,the'nurriber of pieces that can be machined'with agiven tool,'thewear on the tool and the surface finish of the metal being machined because machinists will refuse to work with it.

Hydrocarbon polysulfides containing one or more alkyl or aryl radicals have been suggested as being suitable for addition to lubricating oils in order to produce cutting oils. Tests have shown that some of this class of hydrocarbonpolysulfides, when added to lubricating oils, form compositions having acceptable cutting abilities. Unfortunately, however, most of these hydrocarbon polysulfides, assuch and 'when diluted or blended with a mineral cutting 'oil base, have obnoxious odors that iminediatelydisqualify them as cutting oil-concentrates.

2,790,773 Patented Apr. 30, 1957 ingly'unpleasant'odor thatis characteristic of the-polysulfide itselfrather than of amercaptan impurity, since it cannotbe-alteredbycaustic washing, and diallyl tetrasulfide which,'because of its light yellow color, ready miscibility'with mineral oil and very high sulfur content appeared very promising, was found to have-a nauseating garlic odor. The few polys'ulfides in this groupthat do not possess such odors'initially, almost without exceptiondevelop odors, upon use, that are or soon become so obnoxiousas to cause machinists to walkoff the job. In some instances the "odors developed during use do not seem too unpleaasnt atfirstbut for some reason become intolerable upon continued use due to a subtle accumulation of-odors in high speed, automatic, multi-spindlemachines, because of the-large volumes 'of oil they require and the heat, violent agitation and splashing to which the oil is subjected.

'Proposals'to utilize aryl sulfides incutting oils relate generally tothose -aryl sulfides in which a sulfur atom or a-chain of sulfur atoms is substituted directly on the aromatic nucleus. Thus, for example, proposals have been madeto utilize aryl sulfides, such as phenyl-, tolyl-, Xylyl-, naphthyland anthracenesulfides'in cutting oils without suggesting that there are any material defierences among the many aryl sulfides that would make some of them less suitable than others.

Ithas also been proposed to utilize in cutting oils aryl "sulfides wherein the'sulfur atoms or a chain of sulfur atomsis connectedto the aromatic nucleus by a methene oreth'ene' group. It isbelie'ved, however, that no specific suggestion has been made to utilize such aryl sulfides which have substituted on the aromatic nucleus as many It appears to be generallybelieved in the art thatmonosulfides and disulfides in this more limited class of aryl sulfides are to be preferred over sulfides containing more than'two sulfur atoms because ofgreater'solubility in oilof the monoand disulfides and also becausethe nionoand "disulfides are liquid at or-dinary temperatureswhereas some investigators appear to have concluded that similar but more highly sulfurized compounds are not liquid at ordinary temperatures.

The surprising: andunexpecteddiscovery has now been made that it isfeas'ible to prepare dimethylbenzyl-polysulfides of appreciably higher "sulfur content than'had *ln'therto been con'sidered possible and that diluted or undiluted compositions essentially comprising such "polysulfides, particularly dimethylbenzyl pentasulfide which isdefined herein as having the formula (-(CHalzCbI-IsCHz) 25x wherein xvaries between about 4.5 and 5.5 and preferably" averages about 5,-areeminently suitable as cutting oil concentrates.

Generally, the method of the invention comprises reacting dimethylbenzyl' chloride with sodium tetrasulfide and elemental sulfur at anelevated temperature. The

of (CH3)'2CsHsCH2Cl, is reacted with an excess of sodium :tetrasulfide in the. form of an aqueous solution by agitating the. reactants at an elevated temperature or. the

order er about 200 F; for several 'hoursg preferably' uhder and inert atmosphere such as nitrogen. Upon cooling and settling, the reaction mixture forms an upper organic phase and a lower aqueous phase. The lower aqueous phase is separated ,and the remainder, i. e., the upper organic phase, is washed with an alkali hydroxide solution by stirring at room temperature. Upon separation of the alkali hydroxide solution, high yields of dimethylbenzyl polysulfide containing an average of at least about three and preferably about four sulfur atoms per molecule are obtained.

The reaction between the chloride and sodium tetrasulfide is preferably carried out in the presence of a diluent having a low viscosity and a high flash point. One

such diluent particularly suitable for this purpose is diesel fuel oil. The addition of this hydrocarbon, which does not react with either the reactants, the dimethylbenzyl polysulfide intermediate product or the ultimately desired dimethylbenzyl pentasulfide product, is preferred besulfur for 2 to 3 hours at a temperature above about 200 F. and below about 300 F., preferably about 250 F.

In another embodiment of the method of the invention, which involves a higher consumption of sulfur, the dimethylbenzyl pentasulfide is prepared directly by admixing dimethylbenzyl chloride simultaneously with an excess of sodium tetrasulfide and an excess of elemental sulfur and reacting at a temperature between about 150 F. and about 250 'F. The temperature and time of reaction preferred, to avoid settling out of sulfur from the product upon prolonged standing, are about 200 F. and about 2 /2 hours, respectively. This reaction is likewise preferably carried out under an inert atmosphere such as nitrogen to avoid undesirable darkening of the product and in the presence of a diluent such as diesel fuel oil. Upon cooling and settling, the reaction mixture forms an upper 1 organic phase and a lower aqueous phase. The lower aqueous phase is separated and the remainder, i. e., the upper organic phase including a diluent, if any, is washed with a dilute alkali hydroxide solution by stirring at room temperature. Upon separation of the alkali hydroxide solution, high yields of dimethylbenzyl pentasulfide containing about 4.5 or more sulfur atoms per molecule are obtained.

The exact mechanism of the reaction wherein dimethylbenzyl chloride, sodium tetrasulfide and elemental sulfur are simultaneously admixed and brought to an elevated temperature, is not known. It is believed that the pentasulfide is formed either by a successive reaction of the chloride with the sodium tetrasulfide and then of the resulting polysulfide with the elemental sulfur, by addition of the elemental sulfur to the sodium tetrasulfide and subsequent reaction thereof with the chloride, or by a combination of such steps. It is difiicult to identfy accurately the number of sulfur atoms in each dimethylbenzyl polysulfide and sodium tetrasulfide'molecule. It is possible, however, to determine with accuracy the average number of sulfur atoms in these polysulfides. It is to be understood, therefore, that as used herein the term dimenthylbenzyl pentasulfide is not strictly limited to,

a sulfide containing five sulfur atoms per molecule but is intended to include mixtures of dimethylbenzyl sulfides such as the tri-, tetra-, pentaand hexasulfides wherein the average number of sulfur atoms per molecule is between about 4.5 and 5.5 and is preferably about 5. Similarly, it is to be understood that theterm sodium tetrasulfide, as used herein, is not strictly limited to a' sodium sulfide containing four sulfur atoms per molecule but is intended to include mixtures of sodium sulfides such as the di-, tri-, tetra-, and pentasulfides wherein the average number of sulfur atoms per molecule is at least about 3 and preferably about 4.

The treatment, with alkali hydroxide solution, of the sulfiides, i. e., the intermediate reaction product containing an average of at least about three and preferably about four sulfur atoms per molecule obtained in the first step of the preferred method, and the pentasulfide ultimately obtained by either embodiment of the method, is carried out to wash out mercaptans, hydrogen sulfide, and other remaining chlorides. The use of dilute rather than concentrated alkali hydroxide solutions is desirable to avoid extracting appreciable quantities of sulfur, especially from the pentasulfide products. Aqueous sodium hydroxide solutions having concentrations below 10% are preferred.

It is also desirable to after-treat the washed intermediate reaction product, if any, and the pentasulfide reaction product with a material such as Super Filtrol in order to brighten the product and thereby make it more desirable from an aesthetic point of view.

It is particularly surprising and unexpected, in view of the fact that such closely related homologs as unsubstituted benzyl pentasulfide having the formula (CsHsCHa) becomes increasingly less miscible in cutting oil bases and more unpleasantly odoriferous as x is increased to 5, that cutting oil concentrates essentially comprising dimethylbenzyl pentasulfide are completely miscible in cutting oil bases. Furthermore, the dimethylbenzyl pentasulfide obtained by the method of this invention by itself or in admixture with say by weight of a diluent such as diesel fuel oil, is stable even to the extent that no sulfur will precipitate although the product be stored at 0 C. for several days.

It is also surprising that cutting oils containing concentrates essentially comprising dimethyl-benzyl pentasulfide are stable, have extremely good cutting ability, and neither have nor develop objectionable odor even after considerable use.

The dimethylbenzyl pentasulfide, diluted or not with a suitable diluent such as diesel fuel oil, may be blended with any mineral cutting oil base, preferably an acidtreated oil having a viscosity between about and 300 SSU at F. and containing free sulfur dissolved therein. The lower limit of viscosity specified is imposed largely by sulfur solubility. Oils having viscosities higher than 300 SSU at 100 F. are not preferred because of dilficulties of handling and flowing. Blends containing as littleas 1% by weight of dimethylbenzyl pentasulfide have excellent cutting ability and concentrations of dimethylbenzyl pentasulfide as high as 60% or higher in diesel fuel, without being blended with acid-treated oil, have superior cutting ability and excellent odor characteristics. For cutting operations on difiicult-to-machine ductile steels, blends of mineral cutting oil base containing dissolved elemental sulfur with between about 2 and 5% by weight of the concentrate are highly satisfactory.

It is to be understood that while the products of this invention consist essentially of dimethylbenzyl pentasulfide, preferably diluted with unsulfurized diesel fuel or blended with a mineral cutting oil base having elemental sulfur dissolved therein, or both, conventional additives such as lard oil, graphite, chlorinated wax and the like may be added in amounts that do not materially alter the character of the products.

Steels that are subjected to m'ach ining operations have i a wide degree of machinability. Some result in relatively machining ductile steels.

'2 to 4 hours.

steels, an example of which is SAE C-1137. Other steels include the so-called semiabrasive steels, such as SAE A-4140;

Cutting oils consisting essentially of dimethylbenzyl pentasulfide concentrate, i. e., dimethylbenzyl pentasulfide per se and dilutions thereof, oria blend of the concentrate with a mineral cutting oil base containing dissolved elemental sulfur, are'far superior to any known cutting oil on difiicult-to-machine"ductile steels. However, they are somewhat less satisfactory in the cutting of free-machining ductile steels in'that they appear to reduce tool life in'cutting operations onsuch steels. It has been found that a blend of cutting oil containing about 1 to dimethylbenzyl pentasulfide concentrate with lard oil in an appreciable amount, i. e., above about 1%, materially reduces tool wear and cutting operations on these free- Thus, for example, a cutting oil consisting essentially of a blend of mineral cutting oil base (sulfurized by dissolving 0.8% elemental sulfur) with 1 /2% by weight of a 60/40 mixture of dimethylbenzyl pentasulfide and diesel fuel oil and 4% by weight lard oil has been found to be entirely satisfactory in the cutting of free-machining ductile steels as a cutting oil consisting essentially of the same base blended with 3% by weight of the dimethylbenzyl pentasulfide concentrate.

Thejaddition of an appreciable amount of lard oil, preferably from about 2 to by weight, to cutting oils containing dimethylbenzyl pentasulfide is, therefore, ex-

tremely advantageous where it is desirable to utilize one cutting oil in a variety of machiningoperations, including the cutting of both difiicult-to-machine ductile steels and free-machining ductile steels. Such cutting oils, containing both dimethylbenzyl pentasulfide and lard oil, are also excellent for use in cutting semiabrasive steels. It is to be understood, therefore, that it is within the scope of the invention to blend with dimethylbenzyl pentasulfidecontaining cutting oils varying amounts of lard oil which do materially alter the character of the product.

The advantages and utility of the cutting oil concentrate and cutting oil of this invention, particularly as compared with the properties of cutting oils' commercially available and with premium cutting oils will become more apparent from the following detailed description in the examples.

EXAMPLE 1 Part A 27 parts by weight of dimethylbenzyl chloride were admixed with 52 parts by weight of a 40% aqueous solution of sodium tetrasulfide (approximately a 35% excess of the tetrasulfide to insure complete reaction of the chloride) and with 21 parts by weight of a diesel fuel oil having a viscosity of 34 SSU at 100 F. and a flash point of 180 F. The mixture was agitated at 200 F. for from During the reaction, the refractive index at 25 C. of the organic phase increased from a little below 1.50 to about 1.55 and the density of the organic phase increased from 0.94 to nearly 1.00. The mixture was then cooled and allowed to settle. The lower aqueous phase was separated and the remaining organic phase was treated with one part by volume of 3% aqueous sodium hydroxide solution per 5 parts by volume of organic phase I 6 Part B 3.08 kilograms of the intermediate product were placed in a 4-litre glass beaker and 154 grams of sulfur were added. The mixturewas stirred for 2%. hours at 250 F. The product had'a total active sulfur content of 14.1%, indicating that the x in the pentasulfide of the formula ((CHa)CsHaCH2')2 Sx was equal to 4.96.

EXAMPLE 2 A cutting oilbase was prepared by adding to Diamond Paraffin oil, an acid-treated lubricating oil stock, having an SSU of at 100 F., 0.8% by weight elemental sulfur, i. e., the maximum amount of sulfur soluble in the oil at 0 C. The mixture was heated and stirred at about 200 F. until all of the sulfur was dissolved. This took approximately 1 to 2 hours; A cutting oil was made by blending with the cutting oil base so prepared 3.2% by weight of the '60/40 dimethylbenzyl pentasulfide-diesel fuel oil concentrate prepared as described in Example 1. This cutting .oil was compared for cutting ability in a thread cutting operation with a commercial cutting oil which is a sulfurized mineral oil containing about 3 total sulfur, 1.6% active sulfur, and 4% lard oil. This commercial-cutting oil is one of the best oils available on the marketfor ductile'steel machining.

The cutting oil of the invention and the commercial oil were subjected to tests on the same ductile steel forgings in a thread cutting operation. The finish was taken as the criterion-of tool life, which was considered at an end when either tearing of the thread flank and crest or chip welding at theroot of the chaser land occurred. The results are tabulated in Table I immediately below:

These results show that for ductile'steel machining, the cutting oil of this invention is far superior to the commercial cutting oil considered particularly desirable for such machining operations.

EXAMPLE 3 A cutting oil, referred to in this example as Cutting Oil No. 1, prepared by blending, with the Diamond Parafiin oil containing 0.8% by weight dissolved elemental sulfur that is described in Example 2, 3.0% by weight of the 60/40 dimethylbenzyl pentasulfide-diesel fuel oil concentrate prepared as described in Example 1, was compared in field tests with a cutting oil, referred to in this example as Cutting Oil No. 2, prepared by blending, with the same sulfurized Diamond Paraffin oil, 4.8% by weight of the intermediate product prepared as described in Part A of Example 1 and with the commercial cutting oil described in Example 2. The field tests were carried out on a Browne and Sharpe automatic screw machine with C 1010 steel tubing. The average lives of the form tool and cut-ofi tool, the most perishable tools on the machine, with the different cutting oils were used as a basis for comparison. The results are tabulated in Table II immediately below:

TABLE II Percent Total Average Average 60/40 Percent Form Cutting Cutting Oil Ooncen- Active T001 T001 trate in I Sulfur Life, Life, Oil Hrs. Hrs.

This comparison shows that 3% of the cutting oil concentrate of the invention is equivalent to 4.8% of the cutting oil concentrate prepared as described in Part A of Example 1 and further that cutting oils, prepared by a blending of either of these concentrates in Diamond Parafiin oil in amounts sufficient to give them a total active sulfur constant of about 1.22%, are far superior, in lengthening tool life, to commercial cutting oil having a considerably higher (1.6%) total active sulfur content.

EXAMPLE 4 Three cutting oils were prepared by blending, with the sulfurized Diamond Paraflin cutting oil base described in paragraph 1 of Example 2, 1.5, 3.0 and 4.5%, respectively, of the 60/40 mixture of dimethylbenzyl pentasulfide and diesel fuel oil prepared as described in Example 1. These three cutting oils, therefore, had active sulfur contents of 1.01, 1.22 and 1.42%, respectively.

Three other cutting oils were prepared by blending, likewise with the sulfurized Diamond Paraflin cutting oil base described in the first paragraph of Example 2, with 2.3, 4.6 and 6.9%, respectively, of the 60/40 mixture of dimethylbenzyl polysulfide and diesel fuel oil prepared as described in Part A of Example 1. These other three cutting oils, therefore, also had active sulfur contents of 1.01, 1.22 and 1.42%, respectively.

The six cutting oils so prepared were coded and randomized, and so utilized in tests which involved the threading of pipe in a Toledo pipe threading machine capable of threading A" to 2" pipe, in such a manner that the operators did not know which oil was being tested. The oil was changed every time a new nipple was to be cut and after all the oils had been tested once, a duplicate series of tests was run to eliminate the efiects of differences in pipe. After all the nipples were cut, they were given code numbers and then graded by three, and in some instances two, independent graders as to finish. The factors considered in evaluating finish were roughness of the land and groove surfaces, nicks, and evenness of height and depth of lands and grooves, re spectively.

Of the forty-four ratings made, 27 favored the nipples cut with the cutting oils containing dimethylbenzyl pentasulfide and 17 favored the nipples threaded with the cutting oils containing the concentrate prepared as described in Part A of Example 1. While this may not be justification for concluding that the finish obtainable with a cutting oil having a given active sulfur content,

and containing dimethylbenzyl pentasulfide is superior to the finish obtainable with another cutting oil having the same active sulfur content and containing dimethyl benzyl tetrasulfide, because the laws of probability indicate that the 27:17 score would be possible one time.

200 grams dimethylbenzyl chloride (1.3 tools), 378 grams 40% sodium tetrasulfide solution (0.88 mol. NazSi) 28 grams elemental sulfur (0.88 mol.), and 89 grams of diesel fuel were heated and stirred at 200 F. for 3 hours. The mixture was then cooled and allowed to setlie. The lower aqueous phase was separated and the remaining organic phase was treated with one part by volume of 3% aqueous sodium hydroxide solution to 5 parts by volume of organic phase and the mixture was stirred at room temperature for 30 minutes, the caustic then being separated. Thereupon 3% Super Filtrol was added and the mixture stirred for 10 minutes. The mixture was then filtered to yield 325 grams of a 73/27 mixture of ((CH3)2CsHsCH2) 28x and diesel fuel. 63 grams of diesel fuel was then added 'to the mixture to raise the concentration of diesel fuel therein to 40% Tests showed that the activesulfur content of the 60/40 mixture was 12.4%, indicating that the sulfide contained an average of 4.4sulfur atoms. 7

The fact that the sulfur content of the sulfide prepared by the method of this example did not equal or more closely approach five sulfur atoms per molecule is apparently due to the fact that the treatment of the organic phase with aqueous sodium hydroxide solution tends to extract a considerably larger proportion of active sulfur than it does in the preparation of the corresponding .tetrasulfide. It is apparent, however, that if enough excess elemental sulfur is utilized in the preparation, it may about 60% by weight of a dimethylbenzyl polysulfide having the formula C Hr-S r-CHT- (CH3); (CHa):

wherein x is within the range from about 4.5 to about 5.5, and 40% by weight of diesel fuel oil.

2. A cutting oil consisting essentially of a mineral hydrocarbon oil base containing up to about 0.8% free sulfur dissolved therein and from about 1 to about 5% by weight of a dimethylbenzyl polysulfide having the formula QCHrSr-CHr-Q H1): a):

wherein x is within the range from about 4.5 to about 5.5.

3. A cutting oil consisting essentially of a mineral hydrocarbon oil containing up to about 0.8% free sulfur dissolved therein and from about 2 to about 5% by weight of a dimethylbenzyl polysulfide having the formula (CH3): (CH3):

wherein x is within the range from about 4.5 to about 5.5.

4. A cutting oil consisting essentially of a mineral hydrocarbon oil containing up to about 0.8% free sulfur dissolved therein, from about 1 to about 5% by weight of a dimethylbenzyl polysulfide having the formula (CH1): (CH3):

wherein x is within the range from about 4.5 to about 5.5, and above about 1% up to about 10% by weight, of lard oil.

5. A cutting oil consisting essentially of a mineral hydrocarbon oil containing up to about 0.8% free sulfur dissolved therein, at least about l /2% by weight of a dimethylbenzyl polysulfide having the formula I M (CH2):

wherein x is within the range from about 4.5 to about 5.5, and about 4% by weight of lard oil.

n, wwlr 6. A cutting oil consisting essentially of a mineral hydrocarbon oil containing up to about 0.8% free sulfur dissolved therein and having a viscosity at 100 F. between about 75 and 300 SSU and from about 2 to about 5% by weight of a dirnethylbenzyl polysulfide having the formula wherein x is within the range from about 4.5 to about 5.5,

7. A cutting oil concentrate consisting essentially of a solution in an unsulfurized hydrocarbon diluent of at least about 60% by Weight of a dimethylbenzyl polysulfide having the formula (CHO; HM

wherein x is Within the range from about 4.5 to about 5.5.

References Cited in the file of this patent Ephraim: Inorganic Chemistry, fourth edition, 1947, pages 539-40. 

1. A CUTTING OIL CONCENTRATE CONSISTING ESSENTIALLY OF ABOUT 60% BY WEIGHT OF A DIMETHYLBENZYL POLYSULFIDE HAVING THE FORMULA 